1. Field of the Invention
This invention relates in general to shock absorbers for railway cars, and in particular to an underframe, sliding sill shock absorber.
2. Description of the Prior Art
Rail cars commonly use shock absorbers to avoid excessive shock through the rail car structure and to the lading containing therein. In one type, the shock absorber is located at one end of a rail car and integrated with the coupling structure. In another type, the frame and center or sliding sill will slide relative to each other. The sliding sill is fixed in length, and has coupling ends that protrude past opposite ends of the frame for connecting to other rail cars.
In the sliding sill type, the shock absorber locates underneath the frame within the sliding sill. Various types of shock absorbers have been employed, some employing springs and oil, others employing gas and oil. In the gas and oil type, the shock absorber includes a housing which has an inner cylinder with ports in its sidewall. The inner cylinder has a smaller diameter than the housing to provide an outer reservoir or outer chamber surrounding the cylinder. A piston slides within the inner cylinder, with its shaft extending outward for engaging stops.
In one type of sliding sill rail car, stops are located on the frame and on the sliding sill for providing a limit to the forward and rearward movement of the sliding sill and frame relative to each other. These stops operate independently of the shock absorber. In another sliding sill type, there are no stationary stops that operate independently of the shock absorber. The limit to the forward and rearward travel is handled by the shock absorber itself. Extreme buff movement, resulting in contraction of the piston to the maximum amount, is handled by an internal mechanism.
This type of rail car is no longer being manufactured, however, a relatively large number are still in use. As the original type of shock absorber wears out, a new shock absorber needs to be retrofitted. Without modification, a conventional shock absorber would have no ability to internally operate as a stop for buff movement. If the piston struck the base end of the housing during extreme buff movement, damage would result.